This invention relates to the fusion bonding of thermoplastic articles, and more particularly to an assembly including opposed heating platens extensible to contact and heat a pair of stationary juxtaposed articles immediately prior to their fusion bonding.
Fusion bonding using heated platens is a well known and widely utilized technique for forming strong bonds between parts constructed of fusible plastic. Generally, articles to be bonded are positioned in spaced apart relation to one another with their fusible surface portions aligned and facing one another. A heating platen is interposed between the articles, and the articles are moved against the platen in order to form a fused or plasticized layer in each of the articles. Immediately after heating, the articles are retracted slightly and the platen is withdrawn, whereupon the articles are brought together under pressure, then allowed to cool to complete the fusion bond.
Generally, this process can yield highly satisfactory fusion bonds. Difficulties are encountered, however, where the thermoplastic articles to be bonded are large or bulky, where dimensional tolerances are strict, and where time is at a premium. For example, larger thermoplastic articles require larger fixtures for their support and positioning, increasing the difficulty in meeting strict tolerances for positioning and dimensions. Further, the inertia of larger articles and fixtures increases the difficulty of the rapid or nearly instantaneous reciprocal motion necessary for optimizing certain bonding operations. Consequently, the conventional fusion bonding process, when used to join large, heavy or bulky articles, calls for a compromise between various desirable features such as stability, minimum time and dimensional accuracy.
Therefore, it is an object of the present invention to provide an apparatus particularly well suited for accurate positioning of thermoplastic articles just prior to their fusion bonding, and for rapidly establishing and terminating heating platen contact with such articles.
Another object of the invention is to provide a means for precisely controlling the relative motion of a contact heating platen means and fusible articles as they are heated prior to fusion bonding.
Yet another object is to provide a fusion bonding process for bulky articles which simplifies the pattern of movement of the articles, resulting in a more repeatable, predictable fusion bond.
Yet another object of the invention is to reduce the time required for manipulating heating platens used in the fusion bonding of certain thermoplastic articles.